Open PRAIRIE: Open Public Research Access Institutional Repository and Information Exchange
Abstract
Canada thistle, Cirsium arvense L., is an aggressive invasive species that is found in the northern United States and not easily controlled by chemical and mechanical methods. Integrating biological control agents with other methods may improve control. This study investigated the effects of Canada thistle gall fly (Urophora cardui Diptera: Tephritidae); Canada thistle stem or crown weevil (Ceutorhynchus litura Coleoptera: Curculionidae); Canada thistle bud weevil (Larinus planus Coleoptera: Curculionidae); and Canada thistle tortoise beetle (Cassida rubiginosa Coleoptera: Chysomelidae) on Canada thistle at three SD sites 1997 and 1998, about three years after initial release. Active stem weevil larvae were found in all release sites early in the season (May, June). Bud weevils were found in a limited number of plants in July. Galls and gall fly larvae were found late in the season. Defoliation from the tortoise beetle was not noted at the one site of release. Total nonstructural carbohydrate (TNC) contents of roots were 50% lower in roots from release sites compared to TNC levels in roots from control sites at two locations in 1998. Since Canada thistle infestations rely on roots for survival, reduction of root TNC may be an important mechanism to reduce patch vigor, and ultimately, Canada thistle’s importance in the SD landscape
